The present invention pertains to manual control devices. More specifically, the present invention relates to a selectively engagable manual drive apparatus for use with a normally, automatically powered driving assembly having a moveable member and a stationary member.
Automatically powered driving assemblies such as actuators of the type used to control valves typically employ reciprocating movement of a member such as a piston in a suitable chamber formed by a housing. Actuators of the type described are particularly useful with butterfly or ball valves which employ rotating valve elements.
Piston-cylinder type actuators used for automatic actuation of valves and other various devices typically employ hydraulic or pneumatic power. Since these power sources may from time to time fail, it becomes not only desirable, but in many cases necessary, to provide a means to manually control or override the actuator so as to be able, for example, to open or close the valve which is attached to the actuator. While such manual override means are known, most consume excessive amounts of space, are awkward to operate and are quite expensive.